1. Field of the Invention
The present invention relates to a magnetic recording medium and a method for manufacturing a magnetic recording medium.
2. Description of the Related Art
In recent years, the information-oriented society has become sharply advanced. Magnetic recording apparatuses are typified by a hard disk drive (HDD). Magnetic disks have been required to have a diameter of 2.5 inches and an information recording capacity exceeding 200 gigabytes per disk. In order to meet these needs for magnetic disks, realization of information recording density (areal density) exceeding 200 gigabits per square inch (200 Gbit/in2) is required. A perpendicular magnetic recording system including a double-layer perpendicular medium and a single-pole head can exhibit high recording resolution and therefore, has been researched as a next-generation high-density recording system.
An improvement of the areal density of the magnetic recording disk is achieved by an improvement of the linear density and an improvement of the track density. The improvement of the linear density needs to realize well-balanced three factors, a reduction of magnetic transition region noises of a recording layer, an improvement of thermal stability of recorded signals, and recording ease. For the purpose of realizing them, heretofore, coupled granular and continuous (CGC) media including granular layers and continuous film layers have been proposed (refer to, for example, U.S. Pat. No. 6,468,670 B1).
In such CGC media, magnetic transition region noises can be reduced by using a granular layer as a main recording layer. In the granular layer, nonmagnetic substances have segregated at grain boundaries of magnetic crystal grains. Thus, the influence of the magnetic transition region can be substantially eliminated in the main recording layer. Further, the thermal stability of recorded signals can be improved by using a continuous film layer as an auxiliary recording layer. The continuous film layer has magnetic bonding strength in a direction parallel to a main surface of a substrate, the continuous film layer and the granular layer are magnetically exchange-coupled, and the magnetization of the continuous film layer is pinned by the magnetization of the granular layer. In this manner, an increase in recording density of the CGC medium can be achieved.
In recent years, an exchange spring medium including a soft magnetic layer on a granular layer, an exchange coupled composite, and the like have been known as configurations for performing the function similar to, for example, the function of the continuous film layer of the CGC medium (refer to, for example, IEEETrans. Magn: Vol. 41, No. 10, pp 3166-3168, October 2005). Hereinafter, these configurations are referred to as CGC media and the like. The exchange coupled composite may also be referred to as a hard/stacked medium.